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Free PDF download of CBSE Class 12 Biology revision notes and short key- notes to score more marks in your exams, prepared by expert Biology teachers from. Class 10 Biology Notes are available here. You can read, find and download the notes for the subject of Biology only at BYJU's. Here you can find the notes for. Biology Notes Class XI. As Per CBSE (NCERT) Books. Chapter Wise-Notes PDF (Board Level). One of the main subjects for science students in their class
Offspring produced by sexual reproduction show only the parental characteristics and only sometimes few new recombinants.
Genes are said to be linked when they are located close together on the same chromosome such that they are always inherited together. Sex linked genes These are genes that are located on the sex chromosomes. Gene for a trait may be present, yet offspring does not show the trait. This happens in human females XX where a gene for the trait is recessive.
The female acts as a carrier. In human, sex linked characters found on the X chromosome include: Haemophilia: This is a disease that affects the rate of clotting of blood, leading to excessive bleeding even from a minor cut. Haemophilia is more common in males than in females. A female my have the gene for haemophilia and not show the trait because the normal gene is dominant over the gene for haemophilia.
Such females are referred to as carriers. If the carrier female offspring will be carriers while the other half will be normal. Half the males will be normal and the other heamophilic. Red-green colour-blindness Red-green colour-blindness is caused by a recessive gene found on the X chromosome. It is inherited in the same way as haemophilia.
More males ,, less female 1: million afflicted. It is the inability to distinguish between red and green colours in humans. Genes found on y-chromosome include: Hairy pinna and hairy nose are carried on the Y - chromosome.
Premature balding. Mutations Mutations are sudden changes in the genotype that are inherited. Mutations are rare in nature and mutated genes are usually recessive to the normal wild type genes.
Most mutations are generally harmful and some are lethal. A somatic mutation is a genetic change in somatic cells. Somatic mutations are only inherited if asexual reproduction takes place e. A gene mutation is a change in genes of reproductive cells and is always inherited. The resultant individual is called a mutant.
The mutant has different characteristics from the rest of the population.
Types of Mutations Chromosomal mutations - are changes in number or structure of chromosomes. Gene mutations - also called point mutations - are changes in the chemical nature of the gene. Mutagens: These are agents that cause mutations. The include ultra-violet light, Gamma rays. Certain chemicals e. Causes and consequences of chromosomal mutations There are three main types of chromosomal mutations.
Changes in the diploid number of chromosomes allopolyploidy.
The diploid number changes to 3n triploid or 4n tetraploid and so on. This results from the doubling of the chromosome number in the gamete 2n. This is due to failure of the chromosome sets to separate during meiosis. The phenomenon is known as polyploidy. It is common in plant's and has been employed artificially to produce varieties of crops with hybrid vigour e.
This is allopolyploidy. Change in the total number of chromosomes involving the addition or loss of individual chromosomes autopolyploidy.
This is due to failure of individual chromosomes to separate during meiosis. One gamete gains an extra chromosome while the other loses a chromosome. Non-disjunction results in several disorders in humans: Down's syndrome The individual has 47 chromosomes due to non-disjunction of chromosome It is also known as trisomy The individual has slanted eyes with flat and rounded face, mental retardation and large tongue and weak muscles.
Turner's Syndrome This brings about to a sterile and abnormally short female. It is due to loss of one of the sex chromosomes i. Klinefelter's Syndrome This results in a sterile male who may be mentally retarded. It is due to an additional X chromosome i.
Changes in the structure of a chromosome during meiosis. A portion of a chromosome may break off and fail to unite again or it may be joined in the wrong way or to the wrong chromosome. These mutations are described as follows: Deletion: This is the loss of a portion of a chromosome, Deletion results in individuals born with missing body parts. Inversion: A portion may break from a chromosome and then rejoin to it after turning though an angle-of Duplication: A certain section of an intact chromosome replicates such that the genes are repeated.
Gene Mutations A gene mutation is a change in the structure of a gene. It may involve only a change in one base, e. There are two main type of gene mutations: Due to insertion or deletion of one or more base pairs. Substitution of base pairs e. Genetically inherited disorders in humans Albinism is a mutation that alters the gene responsible for synthesis of skin pigment melanin.
The gene for albinism is recessive. Sickle cell anemia is a common condition in Kenya. Individuals with the sickle-cell gene produce abnormal haemoglobin. It is due to gene mutation caused by substitution of the base adenine for thymine.
The result is the inclusion of the amino acid valine in place of glutamic acid in the haemoglobin synthesised. As a result the red blood cells become sickle shaped when oxygen concentration becomes low i. This leads to blockage of capillaries. Tissues do not get sufficient oxygen. Homozygous individuals are seriously anaemic and die in early childhood. Heterozygous individuals have a mixed population of normal and sickled red blood cells. They are not seriously anaemic and can lead fairly normal lives.
Haemophila bleeder's diseases is due to lack of gene for production of proteins responsible for blood clotting. Practical Applications of Genetics Study of genetics has been put into a wide variety of uses en-compasing plants and animals and in particular humans.
Blood transfusion Blood groups are genetically determined. As discussed earlier a person of blood group A can only get blood from another one of A or O. Plant and Animal breeding Genetics is applied mostly in plant and animal breeding in order to produce varieties that are most suitable to man's needs. This is done through artificial selection. Varieties are developed that are resistant to pests, diseases or harsh climatic conditions.
Genetic counselling Genetic counselling involves advising about hereditary diseases and disorders so that they can make informed decisions. This is done through: Screening for genotypes e. In amniocentesis, cells are obtained from amniotic fluid during pregnancy. Conditions such as Down's syndrome can be detected using microscopy. Genetic Engineering This is a technology that involves the manipulation of the genotype of an organism to get the desired trait.
It also involves the transfer of gene coding for the desired trait from one organism to another. Application of Genetic Engineering Making of hormones e. Human insulin and human growth hormone. Enzymes e. Drugs and vaccines. A variety of tomato with improved paste and a longer shell life. Sheep for producing desired proteins in milk. Plants resistant to pests and diseases. Cloning This is the making of identical copies of genes, DNA and whole organisms.
Cloning is used in plants - that is tissue culture e. The first mammal to be cloned successfully was Dolly - the sheep. A nucleus from the cell obtained from the udder of the sheep was inserted in an unfertilised egg without a nucleus. This zygote was introduced into the uterus of a sheep and developed to full term.
Gene therapy Involves injecting genes into patients of certain diseases e. Parkinson's diseases. The injected gene alters metabolism to bring about the cure of the disease. Practical Activities To demonstrate Continuous variations Height of students Students should work in pairs, use chalk and metre rule to mark level of top of head onto the wall Or door as one student stands straight without shoes, next to the wall or door.
The height for each student is recorded on chalk board. The frequency distribution of height is recording as the height is grouped into various classes. A histogram to represent frequency against height is drawn. The normal bell shaped curve is observed.
Discontinuous variations - ability to roll tongue The number of students who can roll their tongue is recorded as well as the number of non-tongue rollers. Gene for the ability to roll the tongue is dominant, therefore is expected more tongue rollers.
Demonstration of Mitosis and Meisosis Mitosis Plasticene is used to represent number and shapes of various chromosomes e. Each stage of mitosis illustrated e. Centromeres for different chromosomes can be illustrated in different positions.
Each stage of mitosis is illustrated and telophase can be illustrated by surrounding the "chromosomes" with a long many drawn plasticene to represent cell membrane.
It is manipulated to show how telophase takes place. Meiosis The same procedure is followed. Plasticine with contrasting colours is used to show clearly gene mixing in crossing over. Each pair of homologous chromosomes is represented by plasticene with two different colours e. All the steps in the two stages of meiosis are illustrated up to the production of four haploid gametes.
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Human Finger Prints The finger prints for each student's thumb, forefinger and middle fingers of the left hand is imprinted on a white paper. A rubber stamp with ink is used to and each finger -tip phalange is rolled onto the inkpad. For best results students work in pairs. Observations are made at all forefingers, thumb prints and differences noted. The main patterns are noted. It is also noted that no two, fingerprints are exactly similar.
Evolution Meaning of Evolution and Current Concepts Evolution is the development of organisms from pre-existing simple organisms over a long period of time. It is based on the similarities in structure and function that is observed in all organisms. All are made up of cells, and similar chemical compounds are present. This indicates that all organism may have had a common origin. Evolution seeks to explain the diversity of life and also to answer the question as to the origin of life, as well as its present state.
The Origin of Life Human beings have tried to explain how life began. Currently held views are listed below: Special creation -life was created by a supernatural being within a particular time.
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Spontaneous generation life originated from non-living matter all at once. Steady state - life has no origin. Cosmozoan - life on earth originate from elsewhere, outer space. Bio-chemical evolution-life originated according to chemical and physical laws. Only special creation and chemical evolution will be discussed. Special Creation The earliest idea is that of special creation which is recorded in the old testament Genesis 1: It states that God created the world and all living things in six days.
Some hold the six days literally, while others say it may represent thousands of years. According to his theory, the earth and all organisms were created mature. Similarities in structure and function denote the stamp of a "common Designer" Evidence for this view arises from observations of life itself.
Faith explains it all. By faith we understand that the universe was created by the command of God. Several scientists hold this view and their research confirms accounts in the old testament of a universal flood explains the disappearance of dinosaurs as vegetation decreased.
Chemical Evolution The following is the line of thought held in this view to explain origin of life: The composition of atmospheric gases was different from what it is today: There was less oxygen, more carbon IV oxide, hence no ozone layers to filter the ultra-violet light. The high solar energy reached the earth and brought together hydrogen, carbon IV oxide and nitrogen to make organic compounds.
These were: hydrocarbons, amino acids, nucleic acids, sugars, amino acids and proteins. The proteins coalesced and formed colloids. Proteins and lipids formed a "cell membrane" that enclosed the organic compounds, to form a primitive cell. The cell was surrounded by organic molecules that it fed on heterotrophically. This took place in water. From this cell progressively autotrophs evolved. That were similar to blue-green algae. They produced oxygen and as more oxygen was evolved ozone layer formed an blocked ultra violet radiation.
This allowed formation of present day photo-autotrophs. Evidence for Organic Evolution Most of the evidence for evolution is indirect. Direct evidence is obtained from studying the remains of animals and plants of the past. Fossil Records The study of fossils is called paleontology. Fossils are remains of organisms that lived in ancient times.
Most fossils are remains of hard parts of the body such as bones, teeth, shells and exoskeletons. Some fossils are just impressions of the body parts, e.
Fossils are usually found in sedimentary rocks which have been formed by deposition of sediments over millions of years. The deeper the layer of sediments, the older the fossils found in that layer. Modem man, Homo sapiens, evolved from ape-like creatures 25 million years ago.
These evolved to upright, tool using creature called Australopithecus afarensis which had a cranial capacity of cc. This evolved through several intermediates; Homo habilis and Homo erectus to modem day human. Homo sapiens has a cranial capacity of - cc. Homo sapiens is more intelligent. Main features in human evolution include bipedal posture, is an omnivore and has an opposable thumb.
Limitations of the Fossil Evidence Only partial preservation was usually possible because softer parts decayed.
The fossil records are therefore incomplete. Distortion - parts of organisms might have become flattened during sedimentation. Subsequent geological activities e. Geographical Distribution Until about million years ago, all the land masses on earth formed a single land mass Pangaea.
This is thought to have undergone continental drift, splitting into different continents. Consequently, organisms in certain regions became geographically isolated and did not have a chance to interbreed with other organisms in other regions. Such organisms underwent evolution in isolation and have become characteristically different from organisms in other regions.
For example, pouched mammals e. The opossum is the only surviving representative of the pouched mammals in North America. Comparative Embryology During the early stages of development, the embryos of different vertebrates are almost indistinguishable.
Fish, amphibian, bird and mammalian embryos have similar, features, indicating that they arose from a common ancestor. Similarities include: Visceral clefts, segmental muscle blocks myotomes and a single circulation.
Comparative Anatomy Comparative anatomy is the study of organs in different species with the aim of establishing whether the organism are related. Organisms which have the same basic features are thought to have arisen from a common ancestor. The vertebrate pentadactyl limb evolved in different ways as an adaptation to different modes of life. Such organs are said to be homologous, i. This is an example of divergent evolution. The wing of a butterfly and that of a bird are said to be analogous.
This is an example of convergent evolution. Cell Biology All eucaryotic cells have organelles such as mitochondria, membrane-bound nuclei, ribosomes, golgi bodies. Thus indicating that different organisms have a common ancestor. The presence of chloroplasts and cellulose cell walls indicates that green plants have a common ancestor.
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Blood pigments are conjugated proteins with a metal group. Similar pigments are found in different animal groups. This shows that all animals have a common origin. Mechanism of Evolution The mechanism of evolution can be described as a process of natural selection acting on the heritable variations that occur among the members of a population.
A population consists of a group of individuals of the same species. Each individual has a set of hereditary factors genes. All the genes in a population constitute a gene pool. When reproduction takes place, genes pair with one another randomly. Genes which occur in great numbers in the gene pool, will occur in greater numbers in the next generation.
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Several theories have been proposed over the years to explain how evolution took place. By use and disuse of various body parts, the organism would change and acquire certain characteristics. He suggested that these characteristics would them be passed on to the offspring next generation. He proposed that new life forms arise from use and disuse of parts of existing organisms and through the inheritance of acquired characteristics.
The number of young ones is more than the number of adults. More offsprings are produced than can possibly survive. Variation occurs withing a given population,i. On the basis of these observations. Darwin made the following conclusions; There is a struggle for existence among individuals in a given population.
Individuals who are not suitably adapted e. Natural selection operates on the population, selecting those individuals with favourable variations; i.
They win competition e. They attain sexual maturity and pass on the characteristics to their offsprings. Natural selection The peppered moth, Biston betularia, exists in two distinct forms; A speckled white form the normal form and the melanic, dark form.
The moths normally rest on the tree trunks and branches wherre they are camouflaged against predators. The first melanic moths were observed in around Manchester in Britain. Since that time, their numbers has increased tremendously, out-numbering the speckled white form. The increase in the population of the melanic form is correlated with environmental changes brought about by industrialization and pollution.
Smoke and soot from factories have darkened the tree trunks over the years. This has resulted in the preservation of the mutation in Biston betularia leading to the evolution of the melanic form. This form is almost invisible against the dark background of the tree trunks and is less subject to predation than the speckled form.
The peppered form is more abundant in areas away from the soot and smoke of factories. This is because it is well camouflaged by the lichen-covered tree trunks against which it rests and is therefore not easily detected by predators. The existence of two or more distinct forms within a species as exemplified by Biston betularia is called polymorphism. Resistance to Drugs Certain strains of organisms have developed resistance to drugs and antibiotics. Following continued use of such drugs and antibiotics, some of the individuals in a population of bacteria or other microorganisms survive and are able to pass their characteristics to the next generation.
When a patient fails to take full dosage of the antibiotics prescribed the pathogen develops resistance to the drugs hence become difficult to control. Some mosquitoes have developed resistance to certain pesticides.
Practical Activities Limbs of various vertebrates are provided: e. Their anatomy can be studied. The following can be noted: That all limbs have five sets of bones; A single upper bone- the femur in hind limb and the humerus in fore limb Two lower limb bones -i.
Small bones - i. The bones of toes and of fingers i. Limbs of different mammals e. An outdoor activity to observe various sty les of movement in different mammals can be studied.
It is noted that some move on tips of toes donkey others on the whole leg rabbit. Comparision of Wings of bird-and insect Wings of birds and insects grasshopper, butterfly or moth are obtained. A hand lens or a dissecting microscope is used to observe the specimens. The differences in their anatomy is noted. Insect wings are membranous while those of birds are made up of feathers that interlock. The National museum in Nairobi has many fossils. Visit to the various archeological sites that exist in Kenya is recommended.
Reception, Response and Co-ordination In Plants and Animals Introduction The structures involved in detecting the changes may be located far away from the ones that respond. There is need for a communication system within the body. The nervous system and the endocrine system perform this function, i.
Irritability Living organisms are capable of detecting changes in their internal and external environments and responding to these changes in appropriate ways. Lichens, Viruses and Viroids. Salient features and classification of plants into major groups - Algae , Bryophyta, Pteridophyta, Gymnospermae and Angiospermae three to five salient and distinguishing features and at least two examples of each category ; Angiosperms - classification up to class, characteristic features and examples.
Salient features and classification of animals non chordates up to phyla level and chordates up to class level three to five salient features and at least two examples of each category. No live animals or specimen should be displayed. Breathing and Exchange of Gases Respiratory organs in animals recall only ; Respiratory system in humans; mechanism of breathing and its regulation in humans - exchange of gases, transport of gases and regulation of respiration, respiratory volume; disorders related to respiration - asthma, emphysema, occupational respiratory disorders.
Excretory Products and Their Elimination Modes of excretion - ammonotelism, ureotelism, uricotelism; human excretory system - structure and function; urine formation, osmoregulation; regulation of kidney function - renin - angiotensin, atrial natriuretic factor, ADH and diabetes insipidus; role of other organs in excretion; disorders - uraemia, renal failure, renal calculi, nephritis; dialysis and artificial kidney. Locomotion and Movement Types of movement - ciliary, flagellar, muscular; skeletal muscle- contractile proteins and muscle contraction; skeletal system and its functions; joints; disorders of muscular and skeletal system - myasthenia gravis, tetany, muscular dystrophy, arthritis, osteoporosis, gout.
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The Living World What is living? Biological Classification Five kingdom classification; Salient features and classification of Monera, Protista and Fungi into major groups: Plant Kingdom Salient features and classification of plants into major groups - Algae , Bryophyta, Pteridophyta, Gymnospermae and Angiospermae three to five salient and distinguishing features and at least two examples of each category ; Angiosperms - classification up to class, characteristic features and examples.Most fossils are remains of hard parts of the body such as bones, teeth, shells and exoskeletons.
Contact Us. Each axon contains axoplasm which is continuous with the cytoplasm in the cell body. Receptors Receptors are cells that detect or receive stimuli. The bases are represented by their initials as A, G, C and T respectively. ICSE Solutions.
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